1. Field of the Invention
The present invention is directed to a method of manufacturing a crystalline silicon semiconductor film, for example, a polycrystal silicon film, a single crystal silicon film and a microcrystalline silicon film. The crystalline silicon film manufactured by using the present invention is used for various kinds of semiconductor devices.
2. Prior Art
A thin film transistor (hereinafter referred to as TFT) using a thin film semiconductor has been known. This is prepared by forming a thin film semiconductor, particularly, a silicon semiconductor film on a substrate and constituted by using the thin film semiconductor. While TFTs have been utilized in various kinds of integrated circuits, they have been particularly noted as switching elements disposed with each of picture elements or driver elements formed to peripheral circuit portions of an active matrix type liquid crystal display device.
As the silicon film utilized for TFT, it is easy and convenient to use an amorphous silicon film but it involves a problem that the electrical characteristics are much lower than those of single crystal semiconductors used for semiconductor integrated circuits. Therefore, the silicon film has been used only in restricted application uses such as switching elements in the active matrix circuit. The characteristics of TFT may be improved by using thin crystalline silicon films. Those silicon films having crystallinity, other than single crystal silicon, are referred to as a polycrystal silicon, polysilicon, microcrystalline silicon or the like. Such a crystalline silicon film can be obtained by at first forming an amorphous silicon film, and then crystallizing the same by heating (heat annealing). This method is referred to as a solid phase growth method since the amorphous state changes into the crystal state while maintaining the solid state.
It has been confirmed that if an appropriate metal element is added in the step of the solid phase growth, the element functions as a catalyst to promote crystallization. Namely, it has been found that crystallization can be attained at 550.degree. C. and by a treating time for about 4 hours, by depositing one or plurality of elements selected from the group consisting of nickel, palladium platinum, copper, silver, gold, indium, tin, phosphorus, arsenic and antimony (more generally from the elements belonging to the groups VIII, IIIb, IVb and Vb of the periodic table of the former international notation) in a minute amount on the surface of an amorphous silicon film and then heating them (as disclosed in Japanese Patent Laid-Open No. 6-244103, etc.). The No. 6-244,103 corresponds to U.S. Pat. No. 5,639,698.
The orientation of crystals of the silicon film obtained when a catalyst element film is formed uniformly on the entire surface of the amorphous silicon film at random but it has been also known that the crystal orientation can be controlled by selective addition as disclosed, for example, in Japanese Patent Laid-Open No. 7-45519 (which corresponds to U.S. Pat. No. 5,403,772 or No. 7-66425 which corresponds to U.S. Pat. No. 5,534,716). The crystalline silicon film of such uniform crystal orientation has a great worth in view of manufacture of devices, and a method of taking place such crystal growth is called as lateral growth.
However, it is an innegligible problem that the catalyst element introduced in the silicon film gives undesired effects on the electrical characteristics and reliability. It has been generally known that nickel, palladium, platinum, copper, silver and gold, among the catalyst elements, form chlorides and evaporate when heated at a high temperature in an atmosphere containing a halogen compound (particularly, hydrogen halide). However, if they are contained in silicon, since silicon also forms a chloride (dichlor silane or the like) and evaporates, it is difficult to selectively remove only the catalyst element.
For preventing evaporation of silicon, it has been adopted a method of applying heat annealing in an oxidizing atmosphere, thereby forming a silicon oxide layer on the surface of the silicon film, condensing the catalyst element therein and removing the silicon oxide layer thereby removing the catalyst element from the silicon film as disclosed in Japanese Patent Laid-Open No. 7-183538.
A treatment at a high temperature of 700.degree. C. or more is essential for obtaining such silicon oxide and this offsets the effect of low temperature crystallization due to the catalyst element, and it has been demanded for removing the same at a lower temperature.
A method of using a heated silicon will be explained simply with reference to FIG. 2. On a substrate 11, are formed an underlying insulation film 12 such as silicon oxide and an amorphous silicon film 13. A mask film 14 is formed with a material such as silicon oxide or silicon nitride on the amorphous silicon film. An aperture 15 is formed to the mask film 14 for introducing a catalyst element (FIG. 2(A)).
Then, a catalyst element or a catalyst element-containing film (for example, nickel silicide, nickel acetate or the like) 16 is deposited. The deposition means usable herein can include, for example, a sputtering method (Japanese Patent Laid-Open No. 7-45519 and No. 7-66452), gas phase growth method (Japanese Patent Laid-Open No. 7-335548), and spin coating method (Japanese Patent Laid-Open No. 7-130652) (FIG. 2(B)). The Japanese Laid-Open No. 7-130,652 corresponds to U.S. Pat. No. 5,643,826.
Then, when heat annealing is applied at an appropriate temperature, the catalyst element at first crystallizes the amorphous silicon film at a portion 17 just beneath the aperture 15 (FIG. 2(C)).
Subsequently, the catalyst element diffuses laterally along with proceeding of crystallization and crystallizes also a portion 18 apart from the aperture 15 (this referred to as lateral growth) (FIG. 2(D)).
Then, the mask film 14 is removed (FIG. 2(E)).
Then, the silicon film is oxidized at a temperature and in an atmosphere for oxidizing the silicon film to obtain a silicon film 20 in which the concentration of the catalyst element is lowered and a silicon oxide film (thermally oxidized film) 19 in which the concentration of the catalyst element is high. When a halogen-containing gas (for example, silicon chloride) is added in the atmosphere, the catalyst element contained in the thermally oxidized film 19 forms a chloride and is removed (FIG. 2(F)).
The steps described above involve the following drawbacks.
(1) A heat treatment at a high temperature (700.degree. C. or higher) is necessary. PA0 (2) Since the mask film is etched, it has to be taken out once to the outside.